IP block

Everyday user's from a particular isp are not able to access websites from one of my pariticular server, the same problem is presisting some other user's in the same server(I mean they also belong to some other ISP).Apf is installed , but in apf ip block file( /etc/apf/deny_hostrules) is empty.Same client have accounts in our some other server,those all are working fine .Any idea's

That is certainly odd, but I have had reports from clients with similar issues and they had to remove APF. You could still use a static iptables firewall and there are many tutorials and scripts available that can help with that if you check on google.